The present invention relates to bearings for electrically powered devices and in particular to a bearing for supporting the armature shaft of a motor in a power tool that is double-insulated to meet applicable safety standards.
Conventional motor bearings for power tools are typically inserted into rubber boots or sleeves before installation of the bearing into the power tool housing. The rubber boot serves two primary functions: (i) it electrically insulates the motor armature shaft from the power tool housing and adjoining metal components of the motor, and (ii) provides vibration damping of the motor. However, installation of the motor bearings into the rubberized sleeves is a time consuming, manual process. Therefore, it is desirable to provide a unitary bearing assembly that can be directly installed on the motor armature shaft.
The present invention proposes a conventional ball-bearing that has a rubberized sleeve molded directly onto the bearing so that the bearing and insulating rubber boot form a unitary subassembly. To accomplish this objective, the bearing is inserted directly into the mold and the rubberized material is injection molded around the bearing. Importantly, the rubberized material encapsulating the bearing extends around the outer bearing race and along the side faces of the bearing. In a preferred embodiment, separate nylon washers are installed on either side of the bearing when the bearing is inserted into the mold. The rubberized material is then injection molded around the outer bearing race to capture the nylon washers. The preferred embodiment thus prevents the bearing shields on the side faces of the bearing from being subjected to the injection molding pressures within the mold which can deform and thus damage the bearing shields.